Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1999-06-04
2001-06-19
Lipman, Bernard (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S305000, C526S219500, C526S306000, C526S348000, C526S348400
Reexamination Certificate
active
06248838
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to chain entanglement crosslinked polymers manufactured by a method comprising: dispersing at least one monomer and at least one initiator in an immiscible liquid medium to form a fluid dispersion; and decomposing the initiator in the fluid dispersion to activate polymerization and thereby produce chain entanglement crosslinked polymers. The chain entanglement crosslinked polymers of the present invention can be utilized as proppants, as ball bearings, as lubriglide monolayers, and for drilling mud applications.
BACKGROUND OF THE INVENTION
The rigidity of polymers can be enhanced by utilizing high levels or concentrations of polyfunctional crosslinking agents. Most crosslinked polymers can be manufactured by suspension or droplet polymerization where a liquid monomer mixture is dispersed or suspended in an immiscible liquid medium. Suspension polymerization produces spherical polymer particles that can be varied in size by a number of mechanical and chemical methodologies. These methodologies for making crosslinked polymers are well known and practiced in the art of suspension polymerization.
All of the crosslinking agents known in the art are chemical crosslinkers. There are many polyfunctional crosslinking agents in use, but the most prominent crosslinking monomer is divinylbenzene. Divinylbenzene is used to make insoluble, rigid polymers from acrylate esters, methacrylate esters, vinyl acetate, styrene, vinylnaphthalene, vinyltoluene, allyl esters, olefins, vinyl chloride, allyl alcohol, acrylonitrile, acrolein, acrylamides, methacrylamides, vinyl fluoride, vinylidene difluoride, etc. Almost any molecule carrying a carbon-carbon double bond (C═C) can be crosslinked and made rigid by copolymerization with divinylbenzene. Other crosslinking monomers are polyfunctional acrylates, methacrylates, acrylamides, methacylamides and polyunsaturated hydrocarbons.
Another crosslinking methodology known in the art is macroneting. In macroneting, a preformed polymer is swelled in a difunctional reactant and crosslinked with the assistance of a catalyst. An example of macroneting is the crosslinking of polystyrene swelled in a dihalohydrocarbon by the action of a Friedel-Crafts catalyst such as aluminum chloride or ferric chloride.
The beads of this invention differ from the prior art in that the polymeric beads are made rigid and nonelastic by the physical crosslinking of chain entanglement rather than by the chemical crosslinking of polyfunctional monomers.
SUMMARY OF THE INVENTION
In one embodiment, the present invention relates to a polymer made by a method comprising: dispersing at least one monomer and at least one initiator in an immiscible liquid medium to form a fluid dispersion; and decomposing the initiator in the fluid dispersion to activate polymerization and to thereby produce a chain entanglement crosslinked polymer. For purposes of this invention, chain entanglement crosslinking is defined as an irreversible, physical entanglement of polymer chains in which two or more polymer chains are physically intertwined. The term “activate” means to initiate or to start polymerization In another embodiment, the initiator is first added with the monomer to form a mixture and the mixture is dispersed in the liquid medium. In still another embodiment, the initiator has a concentration of greater than 1% of the monomer weight. In yet another embodiment, the method of manufacturing the chain entanglement crosslinked polymer further comprises the step of increasing the concentration of the initiator to increase the level of chain entanglement crosslinking. In a further embodiment, the method further comprises the step of adding at least one chemical crosslinking agent.
In yet another embodiment the level of chain entanglement crosslinking is increased by increasing the number of growing radical chains per minute (or per second) by an accelerating rate of decomposition of the initiator. The accelerating rate of initiator decomposition is accomplished by an escalating temperature ramp, by a catalytic decomposition of the initiator, and/or by photolysis of the initiator.
In still another embodiment, the monomers are olefinic monomers and the initiator are selected from a group consisting essentially of peroxy dicarbonates, diacyl peroxides, peroxyesters, dialkyl peroxides, peroxyketals, ketone peroxides, peroxy acids, azo compounds, photo initiators and mixtures thereof.
In still yet another embodiment, the present invention relates to polymers manufactured by a method comprising: adding at least one monomer with at least one initiator to form a mixture; dispersing the mixture in an immiscible liquid medium to form a liquid dispersion; and decomposing the initiator in the fluid dispersion to activate polymerization and thereby produce chain entanglement crosslinked polymers.
In a further embodiment, the decomposing of the initiator in the manufacturing method is performed by the photolysis of the initiator. For purposes of this invention, photolysis is defined as the use of radiant energy to produce chemical changes including the decomposition of the initiator into radical fragments. In one embodiment, photolysis is conducted using electromagnetic radiation and the frequencies of electromagnetic radiation that can be used effectively for the ultra violet (UV) regions, 10 to 400 nm, in the absence or presence of photosensitizor molecules such as benzophenone and its derivatives, and the x-ray region 0.1-10 nm. Photosensitizor molecules convert single energy states into triplet energy states using the energy transfer to produce free radicals from the initiator molecules more effectively. In another embodiment, photolysis is conducted by a process consisting essentially of UV radiation, gamma radiation, x-ray radiation, electron beam radiation, benzophenone activated UV radiation and mixtures thereof. For purposes of this invention, “radiation” is defined as a process of emitting radiant energy (such as gamma, electron or x-ray) to activate or speed up chemical or physical changes including the initiation of polymerization.
In yet a further embodiment, the decomposing of the initiator in the manufacturing method is performed by catalysis of the initiator. For purposes of this invention, catalysis is defined as a phenomenon in which a relatively small amount of substance augments the rate of a chemical reaction without itself being consumed. In another embodiment, catalysis is conducted using transition metals, halogens, quarternary ammonium salts and lithium halides such as LiCl, LiBr, and LiI. The transition metals are the metals with unfilled d and f orbitals and consist essentially of Cu, Fe, Co, Cr, Ni, Mn, Ce, Mo, Tc, Ru, Rh, Pd, Ag, Re, Os, Ir, Pt, Au and mixtures thereof. The transition metals also includes their various oxidation states. The halogens consist essentially of Cl
2
, Br
2
, I
2
and mixtures thereof
In still yet a further embodiment, the decomposing of the initiator in the manufacturing method is performed by thermolysis of the initiator. For purposes of this invention, thermolysis is defined as the use of heat to produce chemical or physical change. In another embodiment, thermolysis is conducted by heating the fluid dispersion to the ten-hour half-life temperature of the initiator.
In a firer embodiment, the polymer of the present invention further comprises a chemical crosslinking agent.
In another embodiment, the geometry of the polymer can be beads, spheroids, seeds, pellets, granules, and mixtures thereof. In still another embodiment, the polymer of the present invention comprises a combination of low levels of a chemical crosslinking agent and high levels of chain entanglement crosslinking. In a further embodiment, the physical strength of the polymer is a result of both the chain entanglement and the chemical crosslinking agents.
In still a further embodiment, the chemical crosslinking agent of the polymer comprises from about 1.0% to about 100% by weight of the polymer. In one embodiment, the chemical cross
Golub Daniel H.
Lipman Bernard
Sun Drilling Products Corp.
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